1. Field of the Invention
The present invention relates generally to the field of electronic drives for brushless DC motors. More particularly, the invention relates to a novel DC drive package including features or enhanced thermal management of drive circuitry.
2. Description of the Related Art
In the field of electric motor drives, a wide variety of arrangements are known for mounting electronic components and for cooling such components during operation of the drive. In one particular type of motor drive, used to power and control brushless DC motors, a series of solid state power switching devices are used to convert direct current power from a source to pulsed electrical power having a desired frequency or duty cycle. Because the rotational speed of the motor coupled to the drive is a function of the pulse frequency or the duty cycle, the solid state switching devices thus control the speed of the motor by proper regulation of its input power characteristics.
In an increasing number of applications for brushless DC motor drives, there is a need for an integrated drive package which can be assembled with the brushless DC motor. Conventional packaging techniques include a separate drive enclosure which is supported on the outer cylindrical wall of the motor housing, or an add-on unit which is coupled to an end of the preassembled motor. In both techniques, components generating the largest amount of heat, typically the power switching devices, are mounted on circuit boards in rows or lines and are cooled by forced or natural convection. However, depending upon the particular application and on the ambient conditions surrounding the motor and drive, such techniques may provide inadequate cooling for the power switching devices and the other control circuitry, leading to possible overheating and to subsequent degradation and even failure of the drive components. Moreover, the overall package size and configuration is often larger or more encumbering than the user would like, particularly in applications wherein the drive and motors are incorporated into relatively confined spaces, such as machines where the motors are employed to drive fans, blowers, and the like.
In an effort to obtain better cooling of the power electronic devices in such drives, additional fans, circulating devices and heat sinks may be used. For example, in certain known designs, relatively massive heat sinks may be associated with the drive circuit boards in order to extract heat from the power electronic components during operation. Similarly, forced convection fans may be employed in combination with such heat sinks to draw heat from the heat sink surfaces and from the circuit board itself. However, such heat sinks and forced convection devices can add significantly to the cost, size and weight of the overall motor and drive package.
There is a need, therefore, for an improved motor drive which is capable of efficiently transferring heat from circuit components, particularly power electronic devices, in order to more effectively manage heat load generated during operation of the devices. In particular, there is a need for a compact, simple structure for transferring heat from power switching devices in a motor drive that can be incorporated with the drive circuit board, such as in a subassembly of the drive and motor package.